Huang C.,Xinjiang Institute of Ecology and Geography |
Huang C.,Cele National Field Science Observation and Research Station for Desert Grassland Ecology |
Zeng F.,Xinjiang Institute of Ecology and Geography |
Zeng F.,Cele National Field Science Observation and Research Station for Desert Grassland Ecology |
And 6 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2011
Soil organic carbon storage and total nitrogen contents are not only important indicators of soil quality and sustainable crop production, but are also an option for offsetting increasing atmospheric CO 2and N 2O concentrations. Cultivation often causes deterioration of physical soil conditions and reduces nutrient status and humus content, and therefore is considered the main cause of changes in soil organic carbon and nitrogen. Most studies show a decline in soil carbon after cultivation, averaging about 30%. However, some research has suggested that organic carbon contents significantly increase after soils with low natural organic matter levels are converted to cropland. Therefore, soil organic carbon storage and the dynamics of carbon change in cropland have become important issues in evaluating the impact of agricultural management. However, many researchers pay more attention to changes in soil carbon stocks in the plough layer than to changes in deep soil layers. Twenty cropland sites in the Cele oasis, which have been cultivated for up to 100 years, were selected to study the effects of cultivation on changes in the vertical distribution of soil organic carbon, total nitrogen, and available nitrogen by using the method of trading space with time. Based on differences in soil organic carbon and total nitrogen accumulation, five sites representing 100, 80, 30, 15 and 10 years of cultivation were chosen to investigate relationships between crop yield and soil organic carbon or total nitrogen. Soil organic carbon and total nitrogen density in the surface soil layers increased significantly with longtime cultivation. Soil organic carbon densities (0-20 cm) in croplands cultivated for 100, 80, 30, 15 and 10 years were, respectively, 231.7%, 302.9%, 146.3%, 116.6%, and 130. 5% higher than those in an uncultivated desert soil. Corresponding values for total nitrogen density were, respectively, 160. 1%, 217. 6%, 123. 6%, 106. 5%, and 125. 1%. The organic carbon density in deep soil layers (40-200 cm) was also influenced by longtime cultivation, being 36. 4% lower after 30 years' cultivation than that in the desert soil. However, in the 100-year cropland it increased by 52. 0%. Similar results were not found for total nitrogen density. The C/N ratio in the 0-40 cm soil layers of the sites cultivated for 100, 80, 30, 15, and 10 years increased by 28. 3%, 23. 0%, 15.7%, 10.4%, and 6.5%, respectively, compared with that in the desert soil. However, the C/N ratio decreased in deep soil layers of the sites cultivated for 0 to 80 years. Significant negative correlations between C/N ratios and soil available nitrogen in the different soil layers were present only in the desert and 10-year cropland soils. There were significant differences in maize yield in the different croplands. In addition, maize yield was significantly positively correlated with soil organic carbon and total nitrogen density in the 0-200 cm layers, but a corresponding correlation was not found for cotton yield. This suggests that increases in soil organic carbon and total nitrogen were very important for improving maize yield at the Cele oasis, but this was not the case for cotton yield.